System and method for irradiating a target with electromagnetic radiation to produce a heated region

ABSTRACT

A system and corresponding method for irradiating a target with electromagnetic radiation to produce a heated region. The system comprises a coupling device operable to couple electromagnetic radiation from a magnetic resonance imaging system. A plurality of energy radiator applicators are connected to the coupling device to receive electromagnetic radiation energy from the coupling device. Each of the radiator applicators is operable to emit a radio frequency heating signal using the electromagnetic radiation energy from the coupling device. A bolus filled with a dielectric fluid is positioned within the inner area of the MRI system. The bolus is operable to receive the radio frequency heating signals from the plurality of energy radiator applicators and direct the radio frequency heating signals into a section of the body to produce a heated region within the body.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This is a continuation-in-part of U.S. patent application Ser. No.11/286,104 filed on Nov. 22, 2005, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field

The present invention relates generally to systems and apparatus forirradiating targets with electromagnetic radiation, and morespecifically to systems having annular-type or various sectoredapplicators and associated control systems for controlling applicationof radiation to targets through phased array power steering, wherein thephased array system is integratable with a magnetic resonance imagingsystem.

2. State of the Art

Current systems for applying electromagnetic radiation (EMR) to targets,such as living bodies and biological tissue, and controlling theposition of a region of heating within the target through phased arraypower steering are provided with a plurality of electromagneticapplicators powered by multi-channel EMR systems where differentapplicators are each provided with electronically controlled power ofelectronically controlled phase by different power channels of the EMRsystem. This creates a desired phased array heat pattern steeringcapability. Such an approach results in high system complexity and costin order to provide such phased array heat pattern steering. The phasedarray devices have been integrated with magnetic resonance (MR) imagingsystems and operated simultaneous and independent of the MR imagingsystem.

Several types of therapeutic treatments for cancer in humans are incurrent, common use. These treatments include surgery, X-rays, radiationfrom radioactive sources, and chemotherapy. These treatments are oftencombined in various ways to enhance treatment effectiveness.

Although such conventional treatment techniques have been successful intreating cancer in many patients and in prolonging the lives of manyother patients, they are frequently ineffective against many types ofcancer and often have severe adverse side effects at the necessarytreatment levels. Protracted treatment of cancer patients by X-rays orchemotherapy, as an illustration, tends to eventually destroy or inhibitthe patients' natural immunological systems to an extent that manypatients eventually succumb to common infectious diseases, such asinfluenza or pneumonia, which otherwise probably would not be fatal.Also, many patients having advanced stages of cancer or complicationsmay become too weak to withstand the trauma of surgical or other cancertreatments; hence, the treatments cannot be undertaken or must bediscontinued.

Due both to the prevalence and the typically severe consequences ofhuman cancer, as well as frequent ineffectiveness of current treatmentssuch as those mentioned above, medical researchers are continuallyexperimenting in an attempt to discover and develop improved oralternative cancer treatment methods with their associated treatmentapparatus.

Hyperthermia, the generation of artificially elevated body temperatures,has recently been given serious scientific consideration as analternative cancer treatment. Much research has been conducted into theeffectiveness of hyperthermia alone or in combination with othertreatment methods. This research is important in that hyperthermiatechniques appear to have the potential for being extremely effective inthe treatment of many or most types of human cancers, without the oftenseverely adverse side effects associated with current cancer treatments.Hyperthermia is sometimes called thermal therapy indicating the raisingof the temperature of a region of the body.

Researchers into hyperthermia treatment of cancer have commonly reportedthat many types of malignant growths in humans can be thermallydestroyed, usually with no serious adverse side effects, by heating themalignancies to temperatures slightly below that injurious to mostnormal, healthy cells. Furthermore, many types of malignant cell masseshave reportedly been found to have substantially lower heat transfer tolessen the ability to dissipate heat, presumably due to poorervascularity and reduced blood flow characteristics. Consequently, thesetypes of growths appear capable of preferential hyperthermia treatment.Poorly vascular malignant growths can reportedly be heated totemperatures several degrees higher than the temperature reached by theimmediately surrounding healthy tissue. This promises to enablehyperthermic treatment of those types of malignant growths which are nomore thermally sensitive than normal tissue without destruction ofnormal cells, and additionally to enable higher temperature, shorterhyperthermia treatment times of more thermally sensitive types ofmalignancies which exhibit poor vascularity, usually an advantage forimportant medical reasons.

In this regard, researchers have commonly reported that as a consequenceof these thermal characteristics of most malignant growths and thethermal sensitivity of normal body cells, hyperthermia temperatures fortreatment of human cancer should be carefully limited within arelatively narrow effective and safe temperature range. Hyperthermia isgenerally provided by temperatures over 40 degrees C. (140 degrees F.).Hyperthermia has historically included temperatures well above 60degrees C., but in recent years has generally been considered to includetemperatures as high as 45 degrees C. (113 degrees F.). However, theremay be portions of a cancerous tumor that will exceed this level, theintent is to attempt to get as much of the tumor region above the 40degree C. region as possible.

At treatment temperatures above the approximate 45 degrees C. (113degrees F.), thermal damage to most types of normal cells is routinelyobserved if the time duration exceeds 30 to 60 minutes; thus, great caremust be taken not to exceed these temperatures in healthy tissue for aprolonged period of time. Exposure duration at any elevated temperatureis, of course, an important factor in establishing the extent of thermaldamage to healthy tissue. However, if large or critical regions of thehuman body are heated into, or above, the 45 degree C. range for evenrelatively short times, normal tissue injury may be expected to result.

Historically, late in the last century alternating electric currents atfrequencies above about 10 KHz were found to penetrate and cause heatingin biological tissue. As a result, high frequency electric currents,usually in the megahertz frequency range, have since been widely usedfor therapeutic treatment of such common bodily disorders as infectedtissue and muscle injuries. Early in this century, the name “diathermy”was given to this EMR tissue heating technique, and several discrete EMRfrequencies in the megahertz range have subsequently been allocatedspecifically for diathermy use in this country by the FederalCommunications Commission (FCC).

Extensive articles and reports have been written on the use of thephased array principle to provide hyperthermia heat pattern steering,and several patents have been issued covering use of phased arrays. Allhave relied upon the use of electronic phase and power steering toprovide heat pattern steering control. This results in relativelycomplicated equipment configurations with multiple channel controls ofpower and phase. Such configurations can be difficult for routineclinical professionals to learn and utilize in the clinic. The simplerthe clinical controls are in such a treatment system, the easier theoperation of the system and potentially the greater the reliability.Simplicity of such designs may further lead to fewer system failures dueto component failures. The utilization of standardized heating regionsprovided by standard energy steering configurations is expected toprovide improved adaptation for clinical use.

The BSD-2000 system produced by BSD Medical Corporation, Salt Lake City,Utah, utilizes multi-channel phased array systems that controlfrequency, radiated power, and relative phase. Each channel haselectronic controls of power and phase and is connected to differentantennas. This allows electronic steering of the heating pattern, but athigh cost and complexity. Such high cost can be cost prohibitive forroutine clinical use. The ability to do heat pattern steering permitsenergy to be focused and directed more selectively to the target tumorregion. In order to provide sufficient heat energy penetration, a lowerfrequency must be selected. This is because the penetration attenuationof human tissue increases at higher frequencies. As frequency is loweredhowever, the heating focus diameter increases. Thus, the properfrequency is needed to provide the optimum depth within acceptableheating pattern size limits. In general, hyperthermia is best appliedwhen tumor target tissues around the diseased area is also heated. Thisprovides preheating of inflowing blood and reduces thermal conductionfrom the perimeter of the tumor to draw heat out of the tumor perimeter.The BSD-2000 system has been investigated since 1988. The novel use ofsuch phased arrays systems has proven to be useful and beneficial intreating patients with various forms of cancers, even in Phase IIIclinical trials. However, the use of complex and expensive multi-channelamplifier systems to provide multiple EMR synchronous phase energychannels that have phase control to steer the heating region in the bodyhas excessive complexity for routine clinical use in some treatmentcenters. The BSD-2000-3D/MR system is the integration of the BSD-2000-3Dhyperthermia system with a magnetic resonance imaging system. In such aconfiguration the hyperthermia system has been operated independent ofthe MR imaging system, where the MR imaging system has been used as anindependent monitor primarily of temperature. This has been done usingthe proton resonance shift from the image stored prior to body heatingand digitally subtracting the phase image of the initial pattern fromthe complex phase image patterns obtained during heating. This providesgenerally a dominant indication of the temperature change in tissues ofthe body. This temperature change image produced by the MR imagingsystem can include error effects that are produced by tissue perfusionchanges during heating treatments. The perfusion changes can also bedetermined by the MR imaging system.

There is a need for EMR applicator apparatus, and corresponding methodsfor EMR irradiation, which provide simplified heat pattern steering ofEMR heating in a target, such as a target of biological tissue in aliving body or tissue simulating matter.

SUMMARY OF THE INVENTION

It has been observed that the typical operating frequency of a phasedarray device located in a magnetic resonance imaging system can rangebetween 60 to 200 MHz. The typical magnetic imaging system operated witha magnetic field strength of approximately 1.5 Tesla typically usesradio frequency (RF) power transmitters at a frequency of 63.5 MHz. Fora field magnetic strength of approximately 3 Tesla, the transmitterfrequency is typically set to 127 MHz. The high power RF transmitterfrequency of the MR system is in the same range as that used for thephased array hyperthermia device. To simplify such an integrated systemof the phased array hyperthermia with the MR imaging system, it isproposed to provide a novel method to utilize the MR RF power output toalso provide the needed power to heat the target using the phased arrayhyperthermia device that is inserted into the MR aperture.

According to the present invention, a simplified hyperthermia systemutilizing an array of electromagnetic radiation applicators utilizesvariable reflective termination devices coupled to the applicators tocontrol the phase of the EMR power applied to the individual applicatorsto steer and control the position of the system heating region in thetarget. The EMR power can be supplied to the applicators by a single EMRpower source and the phase of the EMR radiation directed toward thetarget by each of the individual applicators is controlled by thevariable reflective termination devices. The state of a variablereflective termination device, e.g., whether the termination presents anopen circuit or a short circuit, can be easily varied by a user of thesystem to control the phase of reflected EMR power at the connection tothe applicator, which controls the phase of the radiation from theparticular applicator. By controlling the phase of the radiation fromeach applicator in this manner, the position of the heated region in thetarget can be steered and controlled without the need for a separatepower channel in the EMR power source for each applicator. A single EMRenergy source with a passive power splitter can be used to supply EMRenergy of approximately equal power and phase to all applicators throughthe power splitter and the phase of energy radiated by each individualapplicator is easily controlled by the variable reflective terminationdevice.

In one embodiment of the present invention, a simplified hyperthermiasystem integrated with a magnetic imaging system having an array ofelectromagnetic radiation applicators utilizes variable reflectivetermination devices coupled to the applicators to control the phase ofthe EMR power applied to the individual applicators to steer and controlthe position of the system heating region in the target and beingenergized by the RF power output of the MR imaging system. The EMR powercan be supplied to the applicators by a single EMR power coupling deviceor by an array of coupling sources that can be inserted into theaperture of the MR imaging system. The phase of the EMR radiationdirected toward the target by each of the individual applicators can becontrolled by the variable reflective termination devices.

The state of a variable reflective termination device, e.g., whether thetermination presents an open circuit or a short circuit, can be variedby a user of the system to control the phase of reflected EMR power atthe connection to the applicator, which controls the phase of theradiation from the particular applicator. By controlling the phase ofthe radiation from each applicator in this manner, the position of theheated region in the target can be steered and controlled without theneed for a separate power channel in the EMR power source for eachapplicator. A single EMR energy coupling device with a passive powersplitter can be used to supply EMR energy of approximately equal powerand phase to all applicators through the power splitter. The phase ofenergy radiated by each individual applicator can be controlled by thevariable reflective termination device. Multiple coupling devices canalso be used to provide the EMR power to individual or groups ofradiating EMR applicators.

In one embodiment, the EMR power source can be coupled to allapplicators in the array. Alternatively, some of the applicators in thearray can be parasitic applicators, i.e., not directly coupled to theEMR power source. These non-active, parasitic applicators can re-radiateEMR energy with the phase of the re-radiated energy dependent upon thetermination of the applicator. The termination can be made adjustable byconnection of a variable reflective termination device coupled to theparasitic applicator. This phase control can also be provided by anumber of means, such as path length variation, and the use of using anumber of PIN diodes that can be turned on to provide a short betweentwo transmission line conductors used for tuning or phase shifting.

In one embodiment, the variable reflective termination devices can becoupled to each applicator in the array. However, depending upon theadjustability of the heating region positioning required or desired, itis not necessary to connect a variable reflective termination device toeach applicator. As a minimum, it is only necessary that one applicatorbe coupled to the EMR power source and that only one applicator beconnected to a variable reflective termination device. If only oneapplicator is coupled directly to the power source, the variablereflective termination device will need to be coupled to a differentapplicator to provide the system with some steering capability. Thecoupling of the applicator(s) to the power source can include use of theEMR power source of a magnetic resonance imaging system by either directcoaxial cable coupling means such as coaxial switches or PIN diodeswitches or by other coupling means from the transmitting body coil.

The applicator array of the invention will usually be formed of aplurality of individual applicators for directing EMR energy toward thetarget. The EMR power source is coupled to supply EMR energy to one ormore of the individual applicators, which are the primary radiators. Thepower source can be controlled to control the amplitude and phase ofenergy supplied by the power source to the primary radiators. The powersource can be a high output power, single channel power source that usesa passive power splitter to activate the primary radiators with EMRpower of approximately equal power and phase. In one embodiment, allapplicators can be primary radiators coupled to the power source throughthe power splitter. Alternatively, some of the applicators can beparasitic non-active, passive radiators that re-radiate EMR energy. Thepower and phase of this re-radiated energy is determined by theterminations of the parasitic applicators. Variable reflectivetermination devices preferably provide the termination of the passiveapplicators and the state of the variable reflective termination devicesdetermine the phase of the re-radiated energy and the resulting heatingpattern of the applicator array.

In one embodiment, four primary radiators are positioned around a targetto be radiated. All radiators are primary radiators coupled to a singlechannel, high power EMR power source through a passive power splitterthat splits the EMR power from the source into four separate channels ofapproximately equal power and phase. The applicators each include atleast one antenna and each have a central energy supply connectionpoint. Each applicator is coupled to the power splitter by a cable ofpredetermined length extending from the power splitter to the applicatorcentral energy supply connection point. Each applicator central energysupply connection point is thus provided with a signal havingapproximately equal power and equal phase through the power splitterfrom the EMR power source. The length of the cable between the centralenergy supply connection point and the variable reflective terminationdevice and the state of the variable reflective termination devicedetermine the apparent state of the central energy supply connectionpoint to incoming EMR power and determines the phase of the EMR energyradiated from the antennas of the applicator. This arrangement providesoffset heat pattern steering toward the surface of the body whilepreserving significant deep heating energy penetration. It providescontrol to direct the region of heating away from a centered region inthe target. For example, in one embodiment, an array of antennas can beused to provide eight offset positions rotated forty-five degrees aroundthe target from one another. The target will usually be a human patientor tissue sample to be heated which is positioned in a housing. Theapplicators can be arranged around the housing to encircle the targetplaced in the housing. A dielectric fluid having an impedanceapproximately equivalent to an applicator impedance at the predeterminedfrequency of the EMR radiation being used in the system can be used tosubstantially fill a predetermined length of the housing around thetarget. The housing will generally include a bolus inside the housingaround the target to contain the fluid.

In another embodiment that would include a magnetic resonant imagingsystem, four or more primary radiators are positioned around a target tobe radiated. All radiators are primary radiators coupled to a single EMRcoupler. The EMR coupler is coupled to the magnetic imaging Body Coilproviding the high power EMR through a passive power splitter thatsplits the EMR power from the MR coupling source into four separatechannels of approximately equal power and phase. The applicators eachinclude at least one antenna and each have a central energy supplyconnection point. Each applicator is coupled to the power splitter by acable of predetermined length extending from the power splitter to theapplicator central energy supply connection point. Each applicatorcentral energy supply connection point is thus provided with a radiofrequency signal having approximately equal power of equal phase throughthe power splitter from the EMR power source.

Each applicator can be connected to a variable reflective terminationdevice through a cable of predetermined length that is also connected tothe central energy supply connection point or to a variable electricallength device such as a variable phase delay transmission devicetypically called a passive phase shifter. The length of the cablebetween the central energy supply connection point and the variablereflective termination device and the state of the variable reflectivetermination device determine the apparent state of the central energysupply connection point to incoming EMR power and determines the phaseof the EMR energy radiated from the antennas of the applicator. Thisarrangement can provide offset heat pattern steering toward the surfaceof the body while preserving significant deep heating energypenetration. It provides control to direct the region of heating awayfrom a centered region in the target. For example, in one embodiment thearrangement can be used to target eight offset positions rotatedapproximately forty-five degrees around the target from one another. Thetarget will usually be a human patient or tissue sample to be heatedwhich is positioned in a housing.

The applicators can be arranged around the housing to encircle thetarget placed in the housing. The EMR coupling device from the magneticresonance imaging system high power EMR amplifier can be either directlyconnected to the applicator array or coupling can be achieved by acoupling device to the body coil in the MR imaging device. The EMRcoupling device can be placed in close proximity to the body coil toprovide for efficient coupling of the EMR power from the body coil. Thecoupling device can utilize the standard activation mode of the bodycoil to pass energy into the coupling device that is directed to theradiating applicator. The connections between the EMR coupler and thefeed points of the applicator phased array can be arranged in such a waythat when the MR transmitting mode is active for image acquisition, theconnections to the applicators are opened so that the applicators do notload the EMR power of the body coil during that time period. Suchopening can be obtained by using PIN diodes to provide an open andclosed circuit path. A dielectric fluid having an impedanceapproximately equivalent to the impedance of the body allows anapplicator impedance to be matched to the body at the predeterminedfrequency of the EMR radiation being used in the system. The bolus canbe used to substantially fill a predetermined length of the housingaround the target. The housing will generally include a bolus inside thehousing around the target to contain the fluid. In one embodiment, thefluid can be deionized water.

Rather than four separate applicators in the system described, a singleapplicator formed by two concentric metallic cylinders surrounding thetarget can be used and can be configured to have the same EMR energysteering as described above. The steering is provided by placingvariable reflective termination devices between the two concentric ringsat spaced intervals around the rings so that the devices can provide anequivalent short circuit termination between the two metal rings tosteer the energy away from the short. This short circuit configurationcan be achieved by joining common ends of the dipoles or filling thespaces partially or totally between the adjacent dipole ends.

The system can utilize different types of EMR applicators to heat thetarget. The individual applicators may be, for example, horn typeradiators, patch radiators, dipole antennae, folded dipoles, monopoles,waveguides, two concentric metal cylinders that surround the target toform a single dipole, etc. These antenna sources can be linearlypolarized for the greatest enhancement of the heating in the overlappingwave targeted region. In another embodiment, circularly or ellipticallypolarized spirals can also be used for the EMR radiating sources.

The system of the present invention can be used to provide lower costand complexity for phased array control of heating patterns inpredictable steering positions in a target through the use of variablereflective termination devices to select and control the reflectiveterminations of at least one of the applicators in an array. In anotherembodiment, the present invention can be included with a magneticresonance imaging system that can provide lower cost and complexity forphased array control of heating patterns in predictable steeringpositions in a target through the use of variable reflective terminationdevices to select and control the reflective terminations of at leastone of the applicators in an array when combined with an magneticresonance imaging system since the expensive high power EMR amplifiersused for the Body Coil can be used for both the imaging and the tissueheating. The variable reflective termination devices can include opencircuit and short circuit terminations, variable cable lengths, orsimilar devices. These devices can also be used to create the sameeffects with parasitic antennas or combinations of primary and parasiticantennas for phase steering of a phased array of antennas. The presentinvention can provide a simplified annular applicator apparatus for EMRheating for any required purpose, such as medical hyperthermic treatmentof cancer or of other medical uses or research.

THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIG. 1 is a schematic diagram of a system of the invention for creatinghyperthermia in a target using active energy at feed points of anantenna applicator array with variable phase terminations used to alterthe resultant phase radiated from each antenna group;

FIG. 2 is a schematic top view of the system of FIG. 1 showing anelliptical target body centrally located inside a cylindrical housingand antenna array;

FIG. 3 is a diagram similar to that of FIG. 1, but showing a phasedarray system with no phase steering capability using a singleelectromagnetic energy source and power splitter that would provide onlya central region of heating within the targeted tissue;

FIG. 4 is a schematic top view of the system of FIG. 3 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the centrally located heated area in thebody;

FIG. 5 is a diagram similar to that of FIG. 1, but showing a phasedarray system with limited phase steering capability with a variablereflective termination device coupled to one of the applicators at itsfeed point so the phase of the termination can be altered to steer theresulting heating pattern created by the system in a body either towardor away from the applicator with the termination device;

FIG. 6 is a schematic top view of the system of FIG. 5 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the steered heated area displaced in thebody away from the applicator with the termination device;

FIG. 7 is a diagram similar to that of FIG. 1, but showing a phasedarray system with limited phase steering capability with a variablereflective termination device coupled to two adjacent applicators attheir feed points so the phase of the termination can be altered tosteer the resulting heating pattern created by the system in a bodyeither toward or away from the applicators with the termination devices;

FIG. 8 is a schematic top view of the system of FIG. 7 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the steered heated area displaced in thebody away from the two adjacent applicators with the terminationdevices.

FIG. 9 is a diagram similar to that of FIG. 5, showing a similar phasedarray system with limited phase steering capability with a variablereflective termination device coupled to a different one of theapplicators at its feed point so the phase of the termination can bealtered to steer the resulting heating pattern created by the system ina body either toward or away from the applicator with the terminationdevice;

FIG. 10 is a schematic top view of the system of FIG. 9 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the steered heated area displaced in thebody away from the applicator with the termination device;

FIG. 11 is a diagram similar to that of FIG. 5, showing a similar phasedarray system with limited phase steering capability with one applicatorhaving only a variable reflective termination device connected at itsfeed point with no connection to the EMR energy source at its feed pointso the phase of the termination can be altered to steer the resultingheating pattern created by the system in a body either toward or awayfrom the applicator with the termination device;

FIG. 12 is a schematic top view of the system of FIG. 11 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the steered heated area displaced in thebody away from the applicator with the termination device;

FIG. 13 is a diagram similar to that of FIG. 7, but showing a phasedarray system with limited phase steering capability with two adjacentapplicators having only a variable reflective termination deviceconnected at their feed points with no connection to the EMR energysource at their feed points so the phase of the terminations can bealtered to steer the resulting heating pattern created by the system ina body either toward or away from the applicators with the terminationdevices;

FIG. 14 is a schematic top view of the system of FIG. 13 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the steered heated area displaced in thebody away from the two adjacent applicators with the terminationdevices;

FIG. 15 is a diagram similar to that of FIG. 11, showing a similarphased array system with limited phase steering capability with adifferent one of the applicators having only a variable reflectivetermination device connected at its feed point with no connection to theEMR energy source at its feed point so the phase of the termination canbe altered to steer the resulting heating pattern created by the systemin a body either toward or away from the applicator with the terminationdevice;

FIG. 16 is a schematic top view of the system of FIG. 15 showing anelliptical target body centrally located inside a cylindrical housingand antenna array and showing the steered heated area displaced in thebody away from the applicator with the termination device;

FIG. 17 is a schematic diagram of a system of the invention with fullsteering capability similar to the system shown in FIG. 1 but showing anapplicator formed of two concentric metal cylinders that surround thetarget forming a single dipole with localized EMR signal feedconnections between the cylinders at four points spaced at ninety degreeintervals around the cylinders and with variable reflective terminationdevices coupled to each feed point between the two cylinders to providesteering similar to that provided by the system of FIGS. 1 and 2;

FIG. 18 is a schematic diagram of a system having a plurality ofelectromagnetic radiation applicators powered by an MRI EMR sourcethrough a switch in accordance with an embodiment of the presentinvention;

FIG. 19 is a schematic diagram of a system having a coupling deviceoperable to couple EMR from a transmitting body coil in an MRI anddirect the EMR to a plurality of electromagnetic radiation applicatorsin accordance with an embodiment of the present invention;

FIG. 20 is a schematic diagram of the system of FIG. 19 showing thetransmitting body coil in relation to the coupling device and theplurality of electromagnetic radiation applicators and a switch used toopen and close the circuit path between the body coil and the couplingdevice;

FIG. 21 is a schematic diagram of the system of FIG. 20 without thevariable reflective termination devices;

FIG. 22 is a schematic diagram of a system having a coupling device thatincludes coupling rings with breaks to couple the EMR from the body coilof the MRI in accordance with an embodiment of the present invention;

FIG. 23 is a schematic diagram of a system having a coupling device thatincludes coupling rings with breaks and resonant coupling dipoles tocouple the EMR from the body coil of the MRI in accordance with anembodiment of the present invention;

FIG. 24 is a schematic diagram of resonant dipole couplers used tocouple the EMR from the body coil of the MRI in accordance with anembodiment of the present invention; and

FIG. 25 is a flow chart depicting a method for irradiating a target withelectromagnetic radiation to produce a heated region in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The apparatus of the invention, as shown in FIG. 1, includes anelectromagnetic radiation (EMR) energy source 10 connected to a powersplitter 11 that splits the EMR energy from source 10 into a pluralityof outputs each connected to one of a plurality of applicators eachincluding one or more antennas 14 connected by cables 17 and havingcentral energy supply connection points 22. The antennas 14 radiate theEMR energy into a body 19, FIG. 2, positioned inside a dielectric shellor housing 20 for heating a target area in the body 19. The radiatedenergy from the antennas is referred to as a radio frequency heatingsignal.

The EMR energy source 10 generally provides EMR energy in a frequencyfrom 40 to 1000 MHz. For heating in human adult torso regions, thepreferred frequencies are from 40 to 200 MHz. This is because thepenetration losses and the localized heating capability at thesefrequencies provide for selective targeting and steering in usefulregions with adequate penetration to heat deeply. The power splitter 11is a passive power splitter configured without internal loss generallyfor more efficient operation. This then provides energy that is directedto an antenna group to be partially or totally reflected with variousphases to alter the location of the phase focusing in the body. The EMRsource 10 is connected to the power splitter 11 using a coaxialtransmission line 9. The power received by splitter 11 is dividedbetween the output coaxial ports, here shown as four coaxial outputports, based upon the impedance presented to the passive power splitterby each of the output coaxial cables 12. The cables 12 are used toconnect the power from the power splitter 11 to the central energysupply connection points or feed points 22 of each applicator, hereshown as four applicators, that are each comprised of single or multipleantennas 14 connected by cables 17. At these feed points 22, there areadditional coaxial cables 16 that are used to attach to variablereflective termination devices 15. These variable reflective terminationdevices control the effective termination seen at the central energysupply connection points 22.

The variable reflective termination devices 15 can be, for example,coaxial shorts or coaxial opens where changing a termination from anelectrical short circuit to an electrical open circuit will alter thereflected phase by one hundred eighty degrees to provide differing phasesteering effects. If the effective termination 15 for example is a shortcircuit and is connected by a cable 16 that is one quarter wave lengthlong, the effect of that short circuit appears as an open circuit at thefeed point 22 and provides for a central focal region of the heatingpattern. This same result will occur if cable 16 is one quarter, threequarters, one and one quarter, one and three quarters, etc. in length.However, when this variable termination is changed to an open circuit atthe end of the quarter wave length cable 16, the resulting heatingpattern is steered away from that applicator or antenna region as theeffective termination at the feed point is that of a short circuit. Inthis case, the energy provided to the feed point 22 from this effectiveshort is reflected back through the coaxial cable 12 to the powersplitter 11. When the reflective energy arrives at the power splitter11, the cable length 12 should be chosen so that the reflected phasefrom the variable termination 22 approximately appears as an opencircuit so that it does not alter the phase or the impedance matching ofother splitter ports, but just reflects its power back to the splitter11 to be redirected out of the other splitter ports. If this reflectedphase from the feed point termination 15 that places a short at the feedpoint 22 would appear as a short circuit at the junction internal to thesplitter 11, then the splitter 11 would reflect too much power back tothe EMR source 10. Therefore, the length of the cables 12 should be aquarter wave length long or an odd multiplier of a quarter wave length(¼, ¾, 5/4, 7/4, 9/4, etc.). This will assure that a short circuit atthe feed point 22 will appear as an open circuit at the splitter 12.When the termination 15 in this example places the equivalent of an opencircuit at the feed point 22, then the impedance from the antenna groupassociated with that channel will reflect a termination impedance of theradiating antennas (typically 50 ohms so the coaxial cable line isimpedance is matched). This reflection that appears as an open circuitat 11 from an effective short termination at the feed point 22 willcause a partial mismatch of impedance in the splitter 11, but this willnot significantly alter the impedance match provided to the EMR source10 for a power splitter 11 having four or more output cables 12.

If the termination example is changed so that cables 16 are an integralnumber of half wavelengths, then the termination to provide an effectiveshort at the feed point 22 would need to be a short circuit. This isbecause a short circuit appears as a short circuit impedance at a halfwavelength from the short termination.

FIG. 2 is a top view of the arrangement of FIG. 1 that shows adiagrammatic cross-sectional view of the elliptical section 18representing the human body as a target for radiation heating. The body18 is surrounded by a housing or high dielectric shell 20 with theapplicators spaced around the shell or housing 20 to surround the targetbody 18. The body 18 is typically surrounded by a high dielectric regionfluid, such as water, filling the space 19 between the target body 18and the dielectric shell 20. Dielectric shell or housing 20 is preferredto be a clear plastic tube. The plastic tube 20 can be cylindrical,elliptical, oval shaped, made by two circular arcs, or in a form ofseveral flat sections such as an octagon or pentagon. Usually a bolusformed by a closed flexible plastic bladder, not shown, is positioned inthe housing 20 around target body 18 to easily hold and contain the highdielectric fluid in the high dielectric region fluid area 19. FIG. 2also shows the four variable reflective phase termination devices 15 asshown in FIG. 1.

FIGS. 3 and 4 are the same as described in the details of FIGS. 1 and 2,but with no variable reflective termination devices 15 of FIGS. 1 and 2.In this arrangement, equal phase is provided at all feed points 22. Thisarrangement without any variable reflective termination devices 15 hasno heating region steering capability and provides only a centralheating region for the apparatus as shown by central heating region 21in body 18 in FIG. 4. This represents and is equivalent to setting allof the variable reflective phase termination devices 15 in FIGS. 1 and 2to provide the same or equal phase at all feed points 22. Such would bethe case, for example, if all four variable reflective terminationdevices 15 in FIGS. 1 and 2 are set to provide an equivalent opencircuit at all feed points 22.

FIG. 4 is a top view of the arrangement of FIG. 3 that shows adiagrammatic cross-sectional view of the elliptical section 18representing the human body. Again, the body is typically surrounded bya high dielectric region fluid, such as water, filling the space 19between the body 18 and the dielectric shell 20, that is preferred to bea clear plastic tube. The plastic tube can be cylindrical, elliptical,oval shaped, made by two circular arcs, or in a form of several flatsections such as an octagon or pentagon. FIG. 4 shows the centralheating region 21 in body 18 that is produced when equal phases areprovided to all applicator feed points 22.

FIGS. 5 and 6 are the same as described in the details of FIGS. 1 and 2,but with only one of the variable reflective termination devices 15 ofFIG. 1. In this arrangement, equal phase is provided at the three feedpoints 22 without the variable reflective termination devices. The phaseat the feed point 22 having the variable reflective termination deviceconnected thereto can be adjusted to provide a different phase from thephase at the other three feed points. This provides steering capability,and when the variable reflective termination device 15 is set to providea different phase from the phase at the other three feed points,provides a displaced heating region 23, FIG. 6, for the apparatus. TheseFIGs. are equivalent to FIGS. 1 and 2 having three of the variablereflective termination devices 15 set to provide the same phase to threeof the feed points 22 and one of the variable reflective terminationdevices 15 set differently to provide a different phase to the fourthfeed point. For example, one of the termination devices in FIGS. 1 and 2can be set to provide a short circuit at the connected feed point 22 andthe remaining termination devices all set to provide an open circuit tothe remaining feed points 22.

FIG. 6 is a top view similar to that of FIG. 4, but shows thearrangement of FIG. 5. The heating zone or region 23 represents theapproximate heating zone that would result from the variable terminationdevice 15 being adjusted to provide an equivalent short circuit at theattached feed point 22 while the remaining feed points 22 are allprovided an equivalent open circuit.

FIGS. 9 and 10 are similar to FIGS. 5 and 6 showing only one of thevariable reflective termination devices of FIG. 1, but showing thevariable reflective termination device connected to a different feedpoint 22 than shown in FIGS. 5 and 6. In this arrangement, as in thearrangement of FIGS. 5 and 6, equal phase is provided at the three feedpoints 22 without the variable reflective termination devices. The phaseat the feed point 22 having the variable reflective termination deviceconnected thereto can be adjusted to provide a different phase from theother three feed points. This also provides a displaced heating region24, FIG. 10, for the apparatus, but the displacement is rotated aboutninety degrees from the displacement provided by the arrangement ofFIGS. 5 and 6 (compare the position of region 24 in FIG. 10 with theposition of region 23 in FIG. 6). These Figures are equivalent to FIGS.1 and 2 having three of the variable reflective termination devices 15set the same to provide the same phase to three of the feed points 22and one of the variable reflective termination devices set differentlyto provide a different phase to the fourth feed point. For example, oneof the variable reflective termination device 15 of FIGS. 1 and 2 can beadjusted to provide a short circuit at the connected feed point 22 andthe remaining termination devices all set to provide an open circuit tothe remaining feed points 22. The comparison of the location of theheating region as steered by the arrangement of FIGS. 9 and 10 and FIGS.5 and 6 show that with the arrangement of FIGS. 1 and 2 where three ofthe variable reflective termination devices provide open circuitterminations and one of the variable reflective termination devicesprovides a short circuit termination, the heating region is displacedaway from the short circuit termination. Thus, with the arrangement ofFIGS. 1 and 2, the heating region can be steered into one of four offsetpositions depending upon which of the four variable reflectivetermination devices is set to provide a short circuit termination whilethe other three variable reflective termination devices are set toprovide open circuit terminations.

FIGS. 7 and 8 are the same as described in the details of FIGS. 1 and 2,but with only two of the adjacent variable reflective terminationdevices 15 of FIGS. 1 and 2. In this arrangement, equal phase isprovided at the two adjacent feed points 22 without the variablereflective termination devices. The adjacent feed points 22 connected tothe variable reflective termination devices 15 can be adjusted toprovide different phases. This provides steering to displace the heatingregion. If both variable reflective termination devices 15 in FIGS. 7and 8 are adjusted to provide a different phase than that provided tothe feed points without the variable reflective termination devices toboth feed points to which they are connected, the heating region 25,FIG. 8, is displaced from both applicators having the variablereflective termination devices 15 coupled thereto. This provides adisplaced heating region 25 in body 18 that is rotated approximatelyforty five degrees in orientation from the position shown in FIG. 6.FIGS. 7 and 8 are equivalent to FIGS. 1 and 2 having two adjacentvariable reflective termination devices set the same to provide the samephase to two of the adjacent feed points 22 and the other two adjacentvariable reflective termination devices set differently to provide adifferent phase or different phases to the other two adjacent feedpoints. For example, two adjacent variable reflective terminationdevices can be set to provide an equivalent open circuit at theconnected feed points 22 and the remaining two adjacent variablereflective termination devices can be set to provide an equivalent shortcircuit to the remaining two adjacent feed points 22. This arrangementwould provide the same displaced heating region 25 in body 18 shown inFIG. 8 that is rotated approximately forty five degrees in orientationfrom that shown in FIG. 6. The particular adjacent pairs of applicatorsin the system of FIGS. 1 and 2 provided with the open circuitterminations and those provided with the short circuit terminationsdetermine in which of four directions the heating region is displaced oroffset.

It should be realized that with the arrangement of FIGS. 7 and 8, if oneof the variable reflective termination devices 15 shown is adjusted toprovide a termination at its connection point the same as at theconnection points without the variable reflective termination devices(three connection points provide the same phase signals) and only one ofthe variable reflective termination devices is adjusted to provide adifferent termination and thus provide a different phase signal at thatone connection point, the system of FIGS. 7 and 8 become equivalent tothe system of either FIGS. 5 and 6 or FIGS. 9 and 10. Therefore, if onlyone of the variable reflective termination devices 15 shown, forexample, the variable reflective termination device 15 at the top rightin FIG. 8, is set to provide a different phase, e.g., that variablereflective termination device is set to provide a short circuit at itsconnection point 22, while the other variable reflective terminationdevice and the two connection points without variable reflectivetermination devices provide open circuit terminations, the apparatus ofFIGS. 7 and 8 become equivalent to the apparatus of FIGS. 5 and 6 andthe deflection of the heating region is as shown in FIG. 6. Similarly,if the variable reflective termination device 15 shown in the lower lefthand portion of FIG. 8 is set to provide a different phase, e.g., thatvariable reflective termination device is set to provide a short circuitat its connection point 22 while the other variable reflectivetermination device and the two connection points without variablereflective termination devices provide open circuit terminations, theapparatus of FIGS. 7 and 8 become equivalent to the apparatus of FIGS. 9and 10 and the deflection of the heating region is as shown in FIG. 10.Further, if both variable reflective termination devices are set toprovide the same termination and same phase signal as the twoconnections without the variable reflective termination devices so thatall applicator connections provide open circuit terminations, the systemof FIGS. 7 and 8 becomes equivalent to the system of FIGS. 3 and 4 withthe heating region centered in the target body. Thus, with the apparatusof FIGS. 7 and 8, variable steering is provided by varying the conditionof the variable reflective termination devices. If both of the variablereflective termination devices provide the same phase terminations asthe two applicators without the variable reflective termination devices(all four applicators have the same phase signals) the heating region issteered to the center of the target body as shown in FIG. 4. If one orthe other or both of the variable reflective termination devicesprovides a different phase termination at its connection point from thephase provided by the two applicators not connected to variablereflective termination devices, the heating region can be easily steeredto the position shown in FIG. 6, the position shown in FIG. 10, or theposition shown in FIG. 8.

With the arrangement of two variable reflective termination devices asshown in FIGS. 7 and 8, and by locating the target body in a particularrotated position within the housing 20, the heated region produced bythe system can be selectively positioned within the body as desired. Inorder to position the heated region in the body without rotationalmovement of the target body in the housing with respect to the twovariable reflective termination devices as described, the system ofFIGS. 1 and 2 with all four connection points being coupled to variablereflective termination devices is preferred. This arrangement of FIGS. 1and 2 allows any one or more of the variable reflective terminationdevices to be set to provide any arrangement of terminations to steer orposition the heated region produced by the system at any selectedposition around the target body. By proper selection of open circuit andshort circuit reflective terminations provided by selected variablereflective termination devices around the body, the system can be madeequivalent to any of the systems of the remaining figures to provide acentral heating region or displaced heating region positioned at anyselected rotated position at forty-five degree intervals around the bodyas described above. If the variable reflective termination devices canprovide a wider range of terminations than merely open circuits andshort circuits, additional steering of the heating region can beobtained. However, the simple open and short circuit connections providea system that is simple to operate and provides a good selection ofsteered heating regions.

FIGS. 11 and 12 are diagrams similar to FIGS. 5 and 6, but show the useof a parasitic applicator which reflects EMR energy back to the target.The parasitic applicator is not connected to the splitter 11 or EMRsource 10, however, it is connected to a variable reflective terminationdevice 15. The approximate position of the resulting heating pattern 26from this arrangement with a single applicator that contains parasiticantennas is shown in FIG. 12 and is similar to that produced by theconnection pattern of FIGS. 5 and 6.

FIGS. 13 and 14 are diagrams similar to FIGS. 7 and 8, but showing theuse of two adjacent parasitic applicators which reflect EMR energy backto the target. The parasitic applicators are not connected to the powersplitter or the EMR source 10, however, they are each connected to avariable reflective termination device 15. The approximate position ofthe resulting heating pattern 27 from this arrangement with two adjacentapplicators each containing parasitic antennae is shown in FIG. 14 andis similar to that produced by the connection pattern of FIG. 8.

FIGS. 15 and 16 are diagrams similar to FIGS. 11 and 12, showing the useof a parasitic applicator which reflects EMR energy back to the target.The parasitic applicator is not connected to the splitter 11 or EMRsource 10, however, it is connected to a variable reflective terminationdevice 15. However, the parasitic applicator with coupled variablereflective termination device 15 in FIGS. 15 and 16 is at a differentlocation than in FIGS. 11 and 12. The approximate position of theresulting heating pattern 28 from this arrangement with a singleapplicator that contains parasitic antennas is shown in FIG. 16 and issimilar to that produced by the connection pattern of both FIGS. 11 and12 and FIGS. 9 and 10.

FIGS. 11 to 16 show that it is not necessary to have a direct connectionof all applicators to the power source. Parasitic applicators willreflect EMR energy and can provide steering capability to the system. Aminimum system with parasitic applicators to provide phase arraysteering would be one primary applicator and one parasitic applicatorwith the parasitic applicator having a variable reflective terminationdevice to adjust the phase of the reflected radiation from the parasiticapplicator. Above that, any selected number of primary and parasiticapplicators could be used. In addition, combinations of primary andparasitic applicators could be used. An example of such a combinationwould be a single primary dipole or monopole antenna device that hasreflective parasitic antennas to each side of the driven or primaryantenna where the side antennas would act as parasitic reflectors basedupon their termination. This could even be single dipoles or monopoleshaving metal strip reflectors to the two sides to form the actualantenna set and the feed point of the dipole or monopole type antennacould have the variable reflective termination device.

FIG. 17 shows an arrangement of the invention where the applicatorcomprises two cylindrical metal rings 14 which extend around the housing20 to enclose the target and a bolus containing a dielectric fluid, suchas water, between the target and the housing walls. A four channel feedsystem for coupling EMR power to the applicator provides four energysupply connection points 22 spaced at ninety degree intervals around therings to provide a balanced feed to the rings. The rings form a singledipole ring applicator. The energy supply connection points 22 are shownas coaxial cables 12 connected to respective rings. Variable phasetermination devices 15 for some or all of the energy supply connectionpoints 22 enable the same heating pattern steering that has been shownby the other figures. The connections of the variable reflectivetermination devices can be placed at each of the energy supplyconnection points and connected to the coaxial cable connections, asshown, can be connected to some of the energy supply connection points,or can be connected to respective rings between the energy supplyconnection points at other positions around the applicator. Further,more than four variable reflective termination devices could be used.The termination devices could include coaxial cables connected to therespective rings 14 or to the coaxial cables 12 at the energy supplyconnection points 22, direct connections between the respective rings,or could be inserts inserted into the space between the respective ringsto create short circuits or other terminations.

While the two cylindrical metal rings of FIG. 17 may be considered orreferred to as forming a single applicator, since the radiation providedor reflected from different locations around the circumference of therings can vary and can be controlled, for purposes of the invention,such an applicator is considered as a plurality of applicators.

It should be realized that with any of the applicators, varioustermination means can be used as the variable reflective terminationdevices. These can be manually operated devices to provide shortcircuit, open circuit, or other connections, such as manually operatedmechanical switches or lengths of coaxial cable manually connected to acoaxial cable connector at the feed points, or can be remotelycontrolled terminations such as controlled by electric coaxial relays,PIN diode termination switches, or other remotely controlled switches ordevices. Further, the termination can be adjusted by using variablecapacitance or other devices, or can be adjusted by adjusting cablelengths coupling a reflective termination device to the feed point. Allof these as well as other means of creating reflective terminations atthe energy supply connection points or other termination points areconsidered as variable reflective termination devices within the scopeof the invention.

The electromagnetic radiation used with the invention should be in theform of radio frequency and microwave energy in order to create thedesired heating regions in the target body.

The applicators can use various antenna configurations such as dipoles,folded dipoles, monopoles, waveguides, parallel strip horns,microcircuit patch antennas, two concentric metal cylinders, etc. Theseantenna radiators provide a dominant linear polarization and aresuitable for providing the deep heating that would be centralized whensuch deep heating is desired. Circularly polarized antennae such asspiral antenna radiators can also be used. However, circularpolarization would not provide as much central heating from an array asa result of the overlapping EMR fields when more than two are used. Thisis because the dominant fields of spirals that are overlapping fromvarying directions will not be co-aligned. It is still possible to usesuch spiral antennas with variable reflective terminations and asparasitic antenna, but the effects on the heating pattern from such willbe different than for the linearly polarized antenna arrays.

While the arrangements of the embodiments of FIGS. 5-16 can be used forsystems which provide limited steering as described for each embodiment,the embodiment of FIGS. 1 and 2 provides a full range of steeringcapability and is thus the preferred system to provide maximum steeringcapability and flexibility to a user of the system. However, while theembodiment of FIGS. 1 and 2 shows all applicators directly coupled tothe EMR energy source, this direct coupling is not necessary for thefull range of steering and flexibility. A system with the full range ofsteering can include parasitic applicators or combinations of primaryand parasitic applicators. The important thing to get the full range ofsteering is to provide a variable reflective termination device coupledto each applicator in the system.

In another embodiment, a simplified hyperthermia system having an arrayof electromagnetic radiation applicators 14 can be integrated with amagnetic resonance imaging (MRI) system and, more particularly, with theMRI system's electromagnetic radiation (EMR) source 91, as illustratedin FIG. 18. The EMR source of the MRI system can be used as the powersource for a hyperthermia system using a phased array or other types ofradiators, as previously described.

In one embodiment, the MRI system's EMR source 91 can be used to supplyan electromagnetic signal to the hyperthermia system applicators 14 byimplementing a switching mechanism 99. The EMR source can be an outputpower amplifier of a magnetic resonance imaging system that is typicallyused to supply high power EMR signals to an MRI system for imagingpurposes. Switching the EMR source between use with the MRI scanner andthe hyperthermia system applicators can be accomplished by a number ofdifferent means. For example, a coaxial relay can be used to switch theEMR source, PIN diode type switching can be used, or another high powerradio frequency means of switching can be incorporated.

The MRI system can be used to form a temperature image. A user candetermine temperature changes caused by the hyperthermia system bytaking a plurality of temperature images with the MRI system. An MRtemperature image may be taken on a periodic basis, such as every tenminutes. It typically takes approximately one minute to obtain the MRimage. Thus, when using the hyperthermia system and the MRI systemtogether, the EMR source 91 can be connected to the hyperthermia systemapplicators 14 a majority of the time.

A typical MRI system includes a receiver configured to detect relativelysmall signals from the specimen that is scanned, typically a person. Dueto the sensitive nature of components within the receive path, such asthe preamplifier, the receive path is typically protected when energy isemitted from the MRI system. The same type of protection may be appliedwhen energy is emitted from the hyperthermia system applicators 14.Disabling the MR receive path from an MRI system body coil or other typeof MR coil can be accomplished using high power PIN diodes to eithershort circuit or open the conductive path to the preamplifier. Most MRIsystem's are already configured to disable the MR receive path whenenergy is emitted from the coil.

In one embodiment, the MRI EMR source 91 can be configured to output anEMR signal having the same frequency to both the MRI body coil and thehyperthermia system applicators 14. When the output is the samefrequency, the MR receive path can be disabled whenever the EMR signalis coupled to either the body coil or the applicators to protect thesensitive receive path devices such as the preamplifier from beingdamaged by the relatively high energy output from the coil andapplicators.

In another embodiment, the MRI EMR source 91 can be configured to outputa different frequency to the hyperthermia system applicators 14. Forexample, the MRI EMR source is typically configured to output an EMRsignal at a frequency of approximately 63.5 MHz for a 1.5T system and127 MHz signal for a 3T system, as previously discussed. When the MRIEMR source is switched to output a signal to the hyperthermia systemapplicators 14, the EMR signal can be set at a different frequency, suchas 100 MHz. Using a different frequency for the hyperthermia systemapplicators can enable passive filtering to protect the MR receive path.The use of passive filtering, such as band pass, band stop, high pass,and low pass filters can enable the hyperthermia system to be poweredwith the EMR signal without the need to disable the MR receive path. Thepassive filtering can be used to substantially filter and thereby blockthe hyperthermia signal frequency from the sensitive receive pathdevices, such as the preamplifier.

When the MRI EMR source 91 is connected to the hyperthermia systemapplicators 14 the signal path can begin at the MRI EMR source, througha transmission means such as a coaxial cable 98, strip line, or othertransmission means, into the switch 99, through another transmissionline 73, and into the splitter 11. The MRI EMR source may include asignal generator, power amplifiers, and filters used to provide asubstantially noise free signal at a desired frequency. The signal canthen be passively spilt at the splitter 11 and directed throughtransmission line 12 to the central energy supply connection points orfeed points 22 of each applicator 14. At these feed points 22, there areadditional coaxial cables 16 that are used to attach to variablereflective termination devices 15. These variable reflective terminationdevices control the effective termination seen at the central energysupply connection points 22 to control the phase at each of theapplicators, thereby enabling the heating location within the MRI systemto be controlled, as previously discussed.

In another embodiment illustrated in FIG. 19, a coupling device such asa capacitive dipole dual coupling ring 97 can be used to couple the EMRsignal in the body coil 94 (FIG. 20) of the MRI system to the couplingring. The coupling ring can be tuned using standard tuning devices suchas capacitors and inductors to enable the coupling ring to be resonantand substantially impedance matched at the operating frequency of theMRI EMR source. The energy coupled from the body coil to the capacitivedipole dual coupling ring can then be directed through transmission line93 a to a switching device 90, along transmission line 93 b, and to thepassive splitter 11. The signal can then be passively spilt at thesplitter 11 and directed through transmission line 12 to the centralenergy supply connection points or feed points 22 of each applicator 14.The use of a coupling device such as the capacitive dipole dual couplingring 97 can eliminate the need for a high power switching device 99(FIG. 18).

The coupling device can be positioned to be sufficiently close to thebody coil within the MRI system to efficiently couple energy from thebody coil. The energy can be passively, radiatively, or inductivelycoupled from the body coil to the coupling device. For capacitivecoupling, the spacing between the body coil and the coupling device canbe within approximately 5 millimeters to provide for strong capacitivecoupling. The actual distance depends on the structure of the body coil.In some MRI systems, the body coil is comprised of relatively longwires. Energy from wires can be radiatively coupled. The rings 97 canact as a radiative coupling device. In one embodiment, the rings can beconfigured as a secondary bird cage type coil that can be inserted intoan MRI system aperture where the body coil is located.

The adult human body, when suspended in a free space environment, willresonate as a dipole conductor when exposed to electric fields that areaxially aligned with the body at a frequency range that has a free spacewavelength that is approximately twice the length of the body. This wasreported by Carl H. Durney and coworkers at the University of Utah on apublished contract to the United States Air Force in February 1978 oncontract report number SAM-TR-78-22. On pages 80 and 81 of this study,it was shown that a typical adult male has a body resonance at afrequency of about 70 MHz and a typical female is resonant at afrequency of about 80 MHz. These results have been used to modify thesafety standards for exposure to such fields. In this report, it wasshown that the total body absorption of the EMR power in an alignedfree-space field at a resonant frequency has an intensity that is fiveto ten times that of either cross polarized fields or fields at muchhigher frequency. In this mode, the body acts as a resonant dipole. Theresonance occurs over a rather broad frequency range. Such bodyresonance creates the strongest electrical currents along the centralregions of the body, with decreasing current for heating at the ends ofthe body.

If one end of the body is touching or close to an effective ground planesuch as the side zone of an MRI scanner, the body resonant behavior canchange to be more like a monopole over the ground plane, changing theresonant frequency to one fourth of a free space wavelength. Thisresults in a quarter wave monopole body resonance for a typical adultmale of 35 MHz and 40 MHz for a typical adult female.

In order to substantially reduce the amount of whole body heating and tobetter focus the EMR emitted from the hyperthermia system applicators14, a bolus containing a high dielectric material can be used. In oneembodiment, the EMR signal directed to the feed points 22 can beradiated from each applicator 14 into a bolus located in the area 19between the target body 18 and the dielectric shell 20 (FIG. 16) of theMRI (FIG. 16). The bolus can be filled with a high dielectric materialsuch as deionized water. The bolus can enable efficient transmissioninto a human body since the body has a similar dielectric constant asdeionized water. The water can act like a dielectric waveguide for theenergy transmitted from the applicators in a similar fashion to lightbeing guided through fiber-optic cables. The use of a water filled bolusclosely connected to the hyperthermia system applicators 14 enables theenergy to be targeted to the tissue region that is intended withoutexposing the whole body to the high level stray electric and magneticfields that can occur without the use of a water bolus.

The bolus can also be useful in cooling of both the whole body and thesurface of the body to keep the skin cool in the presence of the energybeing directed into deeper tissues. Additionally, presence of the waterfilled bolus against the body surface has an additional positive benefitthat it helps to reduce localization of energy near the surface that canresult in superficial hot-spots resulting from anatomical structuressuch as the lower dielectric tissues of fat and bone that are near thesurface.

The displacement currents that are caused to flow in the body by theelectric field emitted from the hyperthermia system applicators 14 tendto follow the relatively high conductivity and high dielectric pathswith decreased currents in the low dielectric fat and bone tissues. Thisphenomenon can result in superficial hot-spots due to localization ofcurrents being displaced by superficial bone and fat structures. Theplacement of a bolus containing high dielectric water against thesurface in these areas provides a high dielectric coupling path forthese displacement currents to flow, which reduces the localization andintensification of these currents in such areas. An example of thelocalization and intensification of currents occurs where the hip boneof the pelvis extends toward the body surface causing a low dielectricbarrier to the displacement currents that can result in intensificationof currents. The currents can concentrate in the high water tissue overand around the bone. Providing a high dielectric surface path using thewater filled bolus substantially reduces the high localization of thecurrents in the high dielectric muscle tissue overlying the boneprotrusion.

In one embodiment, the bolus can have a length that is approximately onewavelength. The wavelength of 100 MHz EMR in water is approximately 33centimeters (cm). For an adult, a typical bolus can have a length around30 to 45 cm long. For a child, or when imaging a portion of a body suchas the leg, the bolus may have a decreased length, around 20 to 30 cmlong. The length can have a range of about 0.5 times to 1.5 times thewavelength of the EMR in the bolus medium. A bolus within this range canprovide sufficient coupling of the energy emitted from the hyperthermiasystem applicators 14 to the body. The use of a water filled bolusprovides a substantial advantage over radiating into an air medium. Thebolus effectively acts as a waveguide, allowing the EMR to be directedto a desired area of the body. In contrast, when the EMR is radiatedinto air, whole body heating typically occurs.

In one embodiment, coupling of the EMR signal from the body coil to thecapacitive dipole dual coupling ring 97 can be achieved by emitting asignal from the MRI EMR source 91 (FIG. 18) to the body coil with aphase that can provide a common voltage field polarization and phase sothat the electric field provided near a central zone by all elements ofthe body coil can have approximately the same orientation and phase.This enables the electric fields coupled to the dual coupling ring to bein phase and therefore additive. Providing a substantially in-phase,additive signal to the dual coupling ring can minimize loading of thebody coil fields. Loading of the body coil fields can create an opposingphase relationship for the electric field in the central zone of thebody coil. It may be necessary in such a case to provide a disconnectmethod such as a PIN diode switch 90. The PIN diode switch, or anotherswitching means, can be used to disconnect the coupling path from thecapacitive dipole dual coupling ring 97 during the MR image transmitmode to avoid image distortions and artifacts due to the presence of theinductive loops of the capacitive dipole dual coupling ring.

FIG. 20 shows the capacitive dipole dual coupling ring 97 describedabove for FIG. 19 with a representation of a body coil 94. FIG. 21 showsthe body coil with the variable reflective termination devices 15removed for additional clarity. The body coil is used to transmit andreceive signals in an MRI system. The body coil is typically astationary fixed part of a magnetic resonance imaging device. The bodycoil can be a bird cage type of MR coil. FIG. 20 shows the MRI EMR powersource 91 can be used to couple energy from the body coil to thehyperthermia system applicators 14 through the coupling rings 97. Theenergy of the body coil 94 can be tightly coupled to the coupling ringsto minimize excessive stray field leakage from the body coil into theair outside the MRI system. The tight coupling of the energy provides anefficient transfer of the typical MR output power to the coupling deviceduring tissue heating mode.

In one embodiment, the MRI system can include a switch 79 that is usedto switch between the transmit and receive modes of the MR system. Aspreviously discussed, the receive path of the MR can be protected duringthe transmit mode. When the MR system is set in receive mode, the switch79 can be opened to prevent the body coil 94 or the hyperthermia systemapplicators 14 from being powered and damaging the sensitive equipmentin the MR receive path.

The capacitive dipole dual coupling ring 97 can be formed from a seriesof dipoles. While a complete ring can be used to couple power from theMR body coil 94, it would likely result in artifacts in the imagingsystem due to currents being induced from the magnetic field emitted bythe MR system. A break 89 in each of the rings can form a dipole systemthat allows the coupling ring to capacitively couple to the body coilwhile minimizing artifacts in the imaging system. A typical dipolesystem can include dipoles that coincide with the position and paths ofthe body coil in the MR system. The dipole system can allow near fieldtransmit and receive coupling between the body coil and the couplingrings.

The EMR signal sent to a body coil 94 in an MR system is typicallyphased to minimize standing waves in an electric field, whichcorresponds to a maximum magnetic field. The EMR signal can be phased tominimize standing waves in the electric field when the EMR from the bodycoil transmission has 180 degrees of phase difference in the centralregion of the body to be imaged. In a standing wave, where the electricfield is minimized the magnetic field will be maximized. The capacitivedipole dual coupling ring 97 is configured to couple the energy toprovide maximum standing waves in the electric field, while minimizingthe magnetic field. When the central energy to produce heating isneeded, the standing wave pattern radiated can provide the peak voltageregion of the standing wave to be in the central region which results ina minima in the magnetic field in that region of the body.

FIG. 22 illustrates a representation of the capacitive dipole dualcoupling ring 97 inside of a typical MR body coil 94. It should be notedthat there are a variety of ways to form a body coil. The coupling ringcan be configured to couple energy from substantially any type of bodycoil. Some types of body coils include wires 75 that run longitudinallyalong the long axis of the body coil. These wires can include tuningcapacitors that help to provide a long axis electric field orientation.A coupling tuner 95 can be used to tune the dipole dual coupling rings97 using tuning capacitors, inductors, and the like to be resonant withthe body coil. Breaks 89 within the rings are used to minimize artifactsin the imaging system, as previously discussed. Coupling paths betweenthe breaks can be formed. In one embodiment, the coupling path can be aTee dipole.

FIG. 23 illustrates that the coupling device can include the capacitivedipole dual coupling ring 97 and also include an array of resonantcoupling dipoles 96 placed inside the body coil 94. The array ofresonant dipoles can be highly coupled and resonant at the body coilfrequency. The resonant dipoles can be joined at the opposite ends tothe coupling rings 97 to form a common coupling device. The energy thatis coupled to the resonant dipoles can be transferred to the centralenergy supply connection points or feed points 22 of each of thehyperthermia system applicators 14. The resonant coupling dipole devices96 can be connected to the feed points 22 through an electronicallycontrolled path length such as a high power phase shifter or a PINdiode. The electronically controlled path length can be used to changethe boundary conditions of the phased array to steer the heatingpattern. Alternatively, short circuits or open terminations alongtransmission lines can be used to control and steer the energy toprovide directional heating capabilities, as previously discussed.

While a single break is illustrated to form resonant dipole couplers 96,multiple breaks may be made in the resonant coupling dipole devices 96.The coupling devices can be positioned to substantially align with theelements of the body coil 94. The length of the elements that make upthe dipoles can correspond with and be positioned with the body coilelements. The body coil elements are typically long axis radiatingelements. The coupling devices, such as the resonant dipole couplers 96can be placed in relatively close proximity with the body coil elementsto provide a high level of radiative coupling. It should be noted thatmultiple breaks 89 are shown in each of the rings of the capacitivedipole dual coupling ring 97. Each of the breaks can include a couplingpath such as a Tee dipole.

FIG. 24 illustrates an additional embodiment in which the resonantdipole couplers 96 are not joined together by the capacitive couplingrings shown in FIG. 23. However, the resonant dipole couplers 96 canstill be used as resonant dipole antennas. The resonant dipole antennasmay be shorter than half wave resonance. At this length, inductorsand/or capacitors can be used to tune the resonant dipole antennas toenable resonant and impedance matching that provides efficient energytransfer from the body coil 94 through the resonant dipole antennas andinto the hyperthermia system applicators 14 to allow for efficientheating at a desired location within a body.

In another embodiment, a method 2500 for irradiating a target withelectromagnetic radiation to produce a heated region is disclosed, asdepicted in the flow chart of FIG. 25. The method includes the operationof coupling 2510 electromagnetic radiation from a transmitting body coillocated in an inner area of a magnetic resonance imaging (MRI) system toa coupling device. The electromagnetic radiation can be coupled usinginductive, capacitive, or radiative coupling. For example, a capacitivedipole dual coupling ring may be used to couple the energy from thetransmitting body coil. An additional operation includes directing 2520the electromagnetic radiation from the coupling device to at least oneof a plurality of energy radiator applicators. The electromagneticradiation can be directed using transmission lines such as coaxialcables, strip lines, and the like. The electromagnetic radiation can bepassively divided using a splitter to divide the energy intosubstantially equal amplitudes having equal phases at one or more of theplurality of energy radiator applicators.

The method 2500 further comprises emitting 2530 a radio frequencyheating signal from the at least one of the plurality of energy radiatorapplicators into a bolus filled with a dielectric fluid and having anopen center region configured to receive a body, wherein the bolus ispositioned within the inner area of the MRI system and is operable toreceive the radio frequency heating signals from the at least one of theplurality of energy radiator applicators and direct the radio frequencyheating signals into a section of the body to produce a heated regionwithin the body. In one embodiment, the dielectric fluid can bedeionized water.

A phase of the radio frequency heating signal from at least one of theplurality of energy radiator applicators can be adjusted using avariable reflective termination device coupled to the energy supplyconnection point of the at least one of the plurality of energy radiatorapplicators. The variable reflective termination device can be adjustedto adjust the phase of the electromagnetic radiation received at theenergy supply connection point to provide the radio frequency heatingsignal with a desired phase relative to radio frequency heating signalsfrom adjacent energy radiator applicators to allow the radio frequencyheating signals to be electronically steered to produce the heatedregion a selected position within the body.

Whereas the invention is here illustrated and described with referenceto embodiments thereof presently contemplated as the best mode ofcarrying out the invention in actual practice, it is to be understoodthat various changes may be made in adapting the invention to differentembodiments without departing from the broader inventive conceptsdisclosed herein and comprehended by the claims that follow:

1. A system for irradiating a target with electromagnetic radiation toproduce a heated region, comprising: a coupling device operable tocouple electromagnetic radiation from a transmitting body coil locatedin an inner area of a magnetic resonance imaging (MRI) system; aplurality of energy radiator applicators having an energy supplyconnection point electrically connected to the coupling device toreceive electromagnetic radiation energy coupled from the transmittingbody coil, with each of the energy radiator applicators operable to emita radio frequency heating signal; and a bolus filled with a dielectricfluid and having an open center region configured to receive a body,wherein the bolus is positioned within the inner area of the MRI systemand is operable to receive the radio frequency heating signals from theplurality of energy radiator applicators and direct the radio frequencyheating signals into a section of the body to produce a heated regionwithin the body.
 2. A system as in claim 1, further comprising at leastone variable reflective termination device coupled to the energy supplyconnection point of at least one of the plurality of energy radiatorapplicators, wherein the variable reflective termination device can beadjusted to adjust a phase of the electromagnetic radiation received atthe energy supply connection point to provide the radio frequencyheating signal with a desired phase relative to radio frequency heatingsignals from adjacent energy radiator applicators to allow the radiofrequency heating signals to be electronically steered to produce theheated region a selected position within the body.
 3. A system as inclaim 1, wherein the plurality of energy radiator applicators are eachantennas selected from the group consisting of horn type radiators,patch radiators, dipole antennas, folded dipoles, monopoles, waveguides,and two concentric metal cylinders that surround the body to form asingle dipole.
 4. A system as in claim 1, wherein at least one of theplurality of energy radiator applicators is a parasitic antenna that isnot actively powered from the coupling device.
 5. A system as in claim1, wherein the coupling device is operable to couple electromagneticradiation from the transmitting body coil using at least one couplingprocess selected from the group consisting of capacitive coupling,inductive coupling and radiative coupling.
 6. A system as in claim 1,wherein the coupling device is a capacitive dipole dual coupling ringconfigured to capacitively couple the electromagnetic radiation from thetransmitting body coil.
 7. A system as in claim 6, wherein thecapacitive dipole dual coupling ring is operable to be tuned to enablethe capacitive dipole dual coupling ring to be resonant andsubstantially impedance matched at an operating frequency of theelectromagnetic radiation coupled from the transmitting body coil.
 8. Asystem as in claim 1, wherein the coupling device is positioned to bewithin a distance of one centimeter from the transmitting body coil ofthe MRI to provide for strong capacitive coupling.
 9. A system as inclaim 6, wherein each ring in the capacitive dipole dual coupling ringis divided into at least two sections, with a coupling path formedbetween each section to minimize artifacts in images produced by the MRIsystem.
 10. A system as in claim 6, further comprising an array ofresonant coupling dipoles joined to at least one of the coupling ringsin the capacitive dipole dual coupling ring coupling device.
 11. Asystem as in claim 10, wherein an electrical path length between one ormore of the resonant coupling dipoles in the array of coupling dipoles,the coupling rings, and the plurality of energy radiator applicators isadjustable using one of electrical and mechanical means to adjust theelectrical path length.
 12. A system as in claim 10, wherein a length ofelements in the array of resonant coupling dipoles are selected tocorrespond with and be positioned adjacent radiative elements in thetransmitting body coil in the MRI.
 13. A system as in claim 1, whereinthe coupling device is operable to be slidably inserted into the innerarea of the magnetic resonance imaging system.
 14. A system as in claim1, wherein the dielectric fluid is deionized water.
 15. A system as inclaim 1, wherein the bolus has a length within a range of 0.5 times to1.5 times a wavelength of the electromagnetic radiation in thedielectric fluid.
 16. A system as in claim 1, wherein the bolus is indirect contact with exposed skin on the body to provide an electricalpath for currents induced in the body to exit through the bolus in orderto reduce localized heating and surface heating of the body.
 17. Asystem for irradiating a target with electromagnetic radiation toproduce a heated region, comprising: a coupling device operable tocouple electromagnetic radiation from an electromagnetic radiationsource of a magnetic resonance imaging (MRI) system having an inner areaoperable to receive a body; a plurality of energy radiator applicatorshaving an energy supply connection point electrically connected to thecoupling device to receive electromagnetic radiation energy from thecoupling device, with each of the energy radiator applicators operableto emit a radio frequency heating signal using the electromagneticradiation energy from the coupling device; a bolus filled with adielectric fluid and having an open center region configured to receivethe body, wherein the bolus is positioned within the inner area of theMRI system and is operable to receive the radio frequency heatingsignals from the plurality of energy radiator applicators and direct theradio frequency heating signals into a section of the body to produce aheated region within the body.
 18. A system as in claim 17, wherein thecoupling device is a switch operable to switch the MRI system'selectromagnetic radiation source between a body coil located in the MRIsystem and the energy supply connection point on at least one of theplurality of energy radiator applicators.
 19. A system as in claim 18,wherein the MRI system's electromagnetic radiation source is operable toemit electromagnetic radiation at a first frequency when the switch isconnected with the body coil in the MRI system and a second frequencywhen the switch is connected with the energy supply connection point onthe at least one of the plurality of energy radiator applicators.
 20. Asystem as in claim 17, wherein the coupling device is a capacitivedipole dual coupling ring used to couple electromagnetic radiation froma body coil located in the MRI system.
 21. A method for irradiating atarget with electromagnetic radiation to produce a heated region,comprising: coupling electromagnetic radiation from a transmitting bodycoil located in an inner area of a magnetic resonance imaging (MRI)system to a coupling device; directing the electromagnetic radiationfrom the coupling device to at least one of a plurality of energyradiator applicators; and emitting a radio frequency heating signal fromthe at least one of the plurality of energy radiator applicators into abolus filled with a dielectric fluid and having an open center regionconfigured to receive a body, wherein the bolus is positioned within theinner area of the MRI system and is operable to receive the radiofrequency heating signals from the at least one of the plurality ofenergy radiator applicators and direct the radio frequency heatingsignals into a section of the body to produce a heated region within thebody.
 22. A method as in claim 21, further comprising emitting a radiofrequency heating signal into a bolus filled with a dielectric fluid,wherein the dielectric fluid is deionized water.
 23. A method as inclaim 21, further comprising emitting a radio frequency heating signalinto a bolus, wherein the bolus has a length within a range of 0.5 timesto 1.5 times a wavelength of the radio frequency heating signal in thedielectric fluid.
 24. A method as in claim 21, further comprisingemitting a radio frequency heating signal into a bolus, wherein thebolus is in direct contact with exposed skin on the body to provide anelectrical path for currents induced in the body to exit through thebolus in order to reduce localized heating and surface heating of thebody.
 25. A method as in claim 21, further comprising adjusting a phaseof the radio frequency heating signal from at least one of the pluralityof energy radiator applicators using a variable reflective terminationdevice coupled to the energy supply connection point of the at least oneof the plurality of energy radiator applicators, wherein the variablereflective termination device can be adjusted to adjust a phase of theelectromagnetic radiation received at the energy supply connection pointto provide the radio frequency heating signal with a desired phaserelative to radio frequency heating signals from adjacent energyradiator applicators to allow the radio frequency heating signals to beelectronically steered to produce the heated region a selected positionwithin the body.